1. Field of the Invention
The present invention relates to a diagnostic method and an apparatus for a channel control apparatus which controls input and output units, depending on commands sent from a central processing unit, through input and output control units (magnetic tape control unit, file control unit, interface control unit, etc.) connected to a common bus in accordance with predetermined interface control procedures and, more particularly, to a diagnostic method and an apparatus for a channel control apparatus which can easily separate a defective part and improve diagnostic performance by providing a pseudo-input/output control unit, which can simulate operations of input and output control units, in the channel control unit.
2. Description of the Related Art
A channel control apparatus controls a variety of input and output control units through a common bus. For example, in a system where a central control unit, a main memory unit and a channel control unit are connected to a multi-path, the input and output control units are connected in series through the channel control unit via the common bus, and the input and output units, such as a printer and a magnetic tape unit are connected to each input/output control unit. In this system, the channel control unit controls the input/output units through the input/output control unit connected to the common bus depending on commands sent from the central control unit, and data transfer control is carried out in a program control mode and a direct memory access transfer mode, etc.
In this system, in the program control mode, data transfer is carried out by controlling the input/output control unit while the channel control unit is connected to the central control unit. While in the direct memory access transfer mode, data transfer is carried out by making an access directly to the main memory unit with the channel control unit connected to the main memory unit.
When the central control unit detects a failure, a diagnostic operation is carried out to detect a defective unit; however, since the input/output control unit connected to the channel control unit through the common bus has a structure corresponding to respective input/output units to which it is connected, a diagnostic method and procedures corresponding to each type of input/output unit are necessary and therefore many test data for diagnosis must be prepared and such data must also be selected during a diagnostic test to correspond to the type input/output unit.
Moreover, if a failure occurs in the common bus continuously due to a failure a driver of the input/output control unit connected to the common bus, it is not possible to perform the diagnostic procedures using the defective the input/output control unit.
As explained above, since the channel control unit of the prior art is mainly composed of a data transfer circuit and a control circuit, a disadvantage results in that failure diagnosis is carried out by operating the input/output control unit through the channel control unit and, as a result, the diagnostic program is complicated and it is very difficult to identify and remove a defective unit connected in series through the common bus.